Soil loss study under contour bunds substitution of different leucaena hedgerow density for soil and water conservation on the upland of upper northern Thailand   Vasuthep Kanchanadul, Putchara Thepa, Priwal Watananukij and Sawasdee Boonchee   ABSTRACT     Soil loss study under contour bund substitution of different  leucaena  hedgerow density had been initiated in 1989,  at Chiangmai Land Development Station, Mae - Rim district, Chiangmai  province in Hang Chat series, 5 percents slope. The treatments comprised of 4 categories as: Contour cultivating peanut  follow  by  mungbean, Growing 4, 8 and 12 rows of leucaena hedgerows in the strip  width of 1.50 m. for the substitution of contour  bunds using horizontal  interval (HI) value equal to  27  meters and between leucaena hedgerow strip contour cultivated with peanut follow by mungbean.       The results of the study during 1989 - 1992 revealed that growing 12 rows of leucaena hedgerows was considered to be the best among the others treatments, it had the lowest rate of soil loss and run off, gave  highest  yield  and economical return, moreover,  it  also improved  soil  fertility and physical properties better than the other treatments. This treatment is excellent and has a  promising prospect to be  introduced  to the farmers in the upland area of approximately  5% slope, on Hang Chat  series and the similar ones in the upper Northern part of Thailand.           Keywords : Soil conservation, Leucaena hedgerow